1. Field of the Invention
The present invention relates to a plant and a process for the aerobic treatment of waste water for the purpose of digesting the organic content thereof and thus reducing its biological oxygen demand (BOD).
2. Description of the Related Art.
Aerobic digestion of waste water, including sewerage, has been used for many years. The process is however expensive and a number of efforts, such as those disclosed in U.S. Pat. No. 4,468,327, have been made to improve on the original "trickle stone" filters first used for this purpose. The present invention is designed to provide a simple, relatively cheap and energy efficient waste water treatment plant and process which will still achieve high levels of BOD reduction. The plant and process according to the present invention are particularly adapted, due to their simplicity and efficiency, for use in small communities where the cost of prior art waste water treatment plants would not have been justified.
It should be noted that many of the prior art plants for the aerobic digestion of waste water include a movable decanter mechanism to decant treated waste water from the plant. Such decanters are expensive and often troublesome involving as they do moving parts. Such movable decanters have been considered necessary for two reasons. Firstly, waste water flows continuously into the plant and the level in the plant varies for this reason. Secondly, upon aeration of the plant the water level rises. The present invention proposes a plant having a fixed outlet which thus avoids the known problems of plants including decanter mechanisms while also avoiding the problems which gave rise to the original use of decanter mechanisms.